Ok, yesterday I had replaced my impeller on my starboard engine. The boat usually runs right at 170*. Now while hooked up to the garden hose its running around 190* and the top of my exhaust risers are too hot to touch while running. You should be able to to put your hands on it and they would be warm, not hot. Also tell its getting too hot as I'm getting alot of steam coming out the exhaust, more so on right side of the engine. Do you think its possibly a bad thermostat and not opening enough to let enough water pass through? Any other ideas are appreciated. I'd hate to just start throwing parts at it and waste alot of money on stuff I don't need. BTW, it's on a 1989 carbed 454ci 330hp. All stock.

Loose the thermostat and see if it gets better , just ran some 454s on the hose in the driveway and they got warm with 9 gallons a minute running thru them ..we took the muffs off and ran it right into the water pump ... good luck

Assuming your old impellor was missing pieces, you may have pieces of the old impellor caught in the thermostat or maybe at an oil cooler. Use a hose and blow water back thru the top of the thermostat housing with a water line disconnected at the sea pump. Someone el may have a better procedure, especially if you old impellor was intact.

Thanks guys. Thing is the other engine is fine on the hose and normally, when I run these engines off a hose it takes 20 minutes just to hit 140*-160* with the cold water. Thats what seems strange to me. And for the impeller it was only missing 2 pieces and were both about 1/2 inch chunks and I felt both of them hit my hand when I pulled the hose off the impeller housing. I'll still backflush though to double check. I'm hoping Its not a stuck exhaust valve or something similar. I did have the carbs off the other day and the lever that goes down in the choke housing could be in wrong (not sure what its called but has the coiled strip in it) and wandering if its in wrong and keeping the engine choked and thats causing it? I'll go see if my cousins boat has the same carb setup and see how the choke lever sets in there later.

This just sucks as I just put in all new carpet and had all my interior re done (got it back Wednesday night) and was ready to head to the lake to enjoy it all. Oh well, what else can you expect from a boat!

If it's been a while since it was run don't forget that some of the passages start clogging up with corosion and that will cause temps to creep up more and more..

It's only been sitting for about a month.

Ok here's a little update. I removed the thermostat and got the choke figured out. Now the temp guage is showing 165* without a thermostat. Ok thats back to normal but the riser still feels too hot. I can't keep my hand on it for more that about 1/2 to 1 second as its too hot. I felt the hose running from the thermostat housing to the exhaust riser and its getting water flow as its nice and cool while running.

I switched the hose to the port engine and its also running 165* or so but the risers are not as hot, nice and warm but I can hold my hand on it.

Buy or borrow a heat infrared thermometer gun to located spots of heat variance engine to engine to pin point the issue. We once found an issue with our Gil manifolds (also supplier to Merc) where the powder coating was breaking away and blocking the water flow....cost $30-$100 at Jeg's or Summit.

Worth having in your tool box:
http://www.sjdiscounttools.com/elect...-infrared.html

Ok I'll see if I can get my hands on one of those and give it a try. Thanks